1. Field of the Invention
The present invention relates to artificial intervertebral disc implants and, in particular, to a multi-chamber balloon implant that inflates to create an oblate spheroid shape.
2. Description of the Background
Intervertebral discs are oblate spherical structures (visibly flattened at the poles and bulging at the equator) that maintain the space between adjacent vertebrae and function as a cushion by absorbing and mitigating forces acting on the spine as a result of daily activities. Each intervertebral disc consists of an outer annulus fibrosus, which surrounds the inner nucleus pulposus. The annulus fibrosus consists of several layers of strong annular fibrocartilage to contain the nucleus pulposus and distribute pressure evenly across the disc. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel that serves to absorb shocks and maintain the intervertebral space as the vertebra move relative to one another.
Deterioration of an intervertebral disc can result from disease, trauma or aging, and results in symptoms including limited mobility, and severe pain. As a result of normal aging the nucleus pulposus loses its ability to retain fluid and contracts in volume resulting in a reduction in the intervertebral space. This reduction may put pressure on the nerves of the spinal column causing pain. Reduction in volume of the nucleus pulposus also reduces the disc's ability to absorb shock which, coupled with age or trauma related weakening of the annulus fibrosus often results in a disc herniation. When the annulus fibrosus tears due to an injury or the aging process, the nucleus pulposus can begin to extrude through the tear. This is called disc herniation, a prolapsed disc or, more colloquially, a slipped or ruptured disc. The bulge of a herniated disc may also put pressure on nearby nerve structures resulting in radiating pain, numbness, tingling, and diminished strength and/or range of motion. In addition, the nucleus pulposus contains proteins which, if extruded from the disc into contact with the neural structures may also cause inflammation and significant pain.
The majority of minor herniated discs will on their own without surgical intervention. Physical therapy and pharmaceutical interventions are often sufficient to manage the condition until this healing can occur. Non-steroidal anti-inflammatory medications are commonly prescribed as are epidural steroid (cortisone) injections, both in conjunction with weight loss and rehabilatory exercise programs. Traditional pain management approaches are also applied. In a significant number of patients surgical intervention is required when these non-invasive techniques are unsuccessful.
A wide variety of surgical options are available including laminectomy and discectomy combined with vertebral fusion and/or dynamic stabilization. However, these surgical options are highly invasive and require prolonged hospitalization and recovery. More recently, artificial disc replacement prosthetics have been used to replace or augment all or part of the removed or resected intervertebral disc. Some such prosthetics use a ball and socket arrangement. For example, U.S. patent application Ser. No. 10/997,823 for “Articulating Spinal Disc Prosthetic” by the inventor herein et al. shows a disc prosthetic including a superior (upper) plate, inferior (lower) plate, and intermediate layer, in a sandwich. The intermediate member is sandwiched between the superior and inferior plate members with conforming sides, and includes a short cylindrical post protruding downward into a circular recess in the inferior plate member to center it and to maintain a predetermined spacing there between. The post includes snap-in spring fingers that lock into the recess of the inferior member to prevent withdrawal.
There are also a variety of spring discs that employ springs sandwiched between metal endplates. For example, U.S. Pat. No. 5,458,642 to Beer et al. issued Oct. 17, 1995 shows a synthetic intervertebral disc for implantation in the human body. The disc is comprised of disc-shaped plates 11 joined by springs along the inside. The spring system distributes forces acting on the disc between the springs and allows normal movement of the vertebrae during flexion and extension of the spine in any direction.
Still other disc prosthetics are soft cushions with material properties more similar to the discs that they replace. Examples of such disc replacements are disclosed in U.S. Pat. Nos. 5,702,450 and 5,035,716, which employ elastic cushion “formed of a disk material with mechanical properties as similar as possible to the properties of a natural disk.”
The general concept of an expandable balloon-like artificial disc prosthesis filled with a polymer such as silicone is well known. Some of these fixate externally to the vertebrae. For example, United States Patent Application 20060085074 by Raiszadeh, Kamshad published Apr. 20, 2006 shows an expandable intradiscal prosthetic configured to be placed between two vertebrae.
United States Patent Application 20070250169 by Lang, Philipp published Oct. 25, 2007 shows a joint arthroplasty device formed in situ by inserting a hollow device having an aperture and a lumen into a target joint, and injecting material into the hollow device to form an implant.
United States Patent Application 20070135922 by Trieu, Hai H. published Jun. 14, 2007 and his issued U.S. Pat. No. 7,182,783 issued Feb. 27, 2007 both show selectively expandable composite structures useful as spinal arthroplasty devices. The structures comprise an outer shell comprised of a non-hydrogel polymer material. At least one core is positioned within the outer shell and this may be comprised of a hydrophilic polymer. The core expands upon hydration, thereby deforming the outer shell.
United States Patent Application 20070073290 by Boehm, Frank H. JR. published Mar. 29, 2007 shows an artificial/prosthetic facet joint with ballotable/compressible joint space component composed of latex, polymer, silicone, or any other substance either previously used in the art or not. This flexible outer surface contains within it, a ballottable fluid or gelatinous center.
United States Patent Application 20060241759 by Trieu, Hai H. (SDGI) published Oct. 26, 2006 shows oriented polymeric spinal implants wherein the polymer material is substantially uniformly oriented for increased strength perpendicular to the orientation of the polymer material.
United States Patent Application 20060206209 by Cragg et al. published Sep. 14, 2006 shows a prosthetic nucleus replacement for treating an intervertebral disc. A barrier sealant membrane is deposited on a tissue surface within a de-nucleated space within an intervertebral disc. This is filled with a prosthetic nucleus material.
United States Patent Application 20050149191 by Cragg et al. published Jul. 7, 2005 shows a spinal mobility preservation apparatus with a proximal body, an intermediate body, a distal body, and an expandable membrane. The expandable membrane extends into the intervertebral disc space to support the spinal motion segment.
United States Patent Application 20040186576 by Biscup et al. (SpineCo.) published Sep. 23, 2004 shows a prosthetic implant for forming a support structure between adjoining vertebrae in a spinal column. The prosthetic implant includes a generally spherical or ellipsoidal body that at least partially engages a surface of adjacent vertebrae.
United States Patent Application 20030055506 by Stoy et al. published Mar. 20, 2003 shows a hydrogel-based prosthetic device for replacing at least a part of the nucleus of a spinal disc. The prosthetic device is composed of at least two essentially parallel soft layers of an elastically deformable hydrogel and at least one rigid layer, the rigid layer having less compressibility than the soft layers, being adjacent to the soft layers, parallel to them, and firmly attached to them.
U.S. Pat. No. 7,128,746 to Singer et al. (PMT Corporation) issued Oct. 31, 2006 shows a method and device for treating human intervertebral disc herniations using an endoscopic procedure. An access port is opened into and through the annulus of a disc to remove nucleus pulposus. A balloon device having a valve structure is positioned via an endoscopic procedure into the disc space, and the balloon device is filled with a physiological fluid to occupy the disc interspace or to maintain some degree of distraction of the created disc space.
U.S. Pat. No. 7,066,960 to Dickman issued Jun. 27, 2006 shows an intervertebral disk prosthesis formed of a matrix of bioincorporable fabric impregnated with a nuclear core mixed into the matrix and hardened. The core is a polymer, preferably of liquid form that cures into a viscoelastic solid, in which each component—polymer and fabric—reinforces the other against tearing, shearing and weakening under stress. Each edge of the outer fabric that interfaces a vertebral end plate is impregnated with an agent to stimulate osseus incorporation and anchoring.
United States Patent Application 20030033017 by Lotz et al. (Univ. of California) published Feb. 13, 2003 shows a nucleus implant for repairing degenerated intervertebral discs that is inflated inside the nucleus space after the degenerated nucleus has been removed to re-pressurize the nuclear space within the intervertebral disc. The implant is inflated with a high molecular weight fluid, gel or combination of fluid and elastomer, through a self-sealing valve that allows one-way filling of the implant after it is placed within the disc.
Finally, United States Patent Application 20050033437 by Bao et al. (Pioneer Laboratories, Inc.) published Feb. 10, 2005 shows an artificial disc device for replacing a damaged nucleus. The device may be inserted into the natural annulus in a collapsed or compressed state or arrangement and then be expanded. Many variations are shown, one (FIG. 34) including opposing spacer plates coupled together at a canister 220 with telescoping walls. The canister may be filled with fluid, or may be filled with elastomeric material, or a balloon.
However, none of the preceding inventions presents an ideal replacement for the natural intervertebral disc is supplants. An ideal replacement would mimic the properties of the natural disc by maintaining the intervertebral disc space through a full range of natural motion, absorb the shocks of daily use, permit a natural range of motion and yet resist hyper extension of the joint, limit wear so as to extend the useful life of the implant, be collapsible or compressible so as to be implantable through minimally invasive techniques and be simple to manufacture and assemble.